According to an OCV disclosed in JP-2001-187979A, a spool of a spool valve is displaced axially by means of an electromagnetic actuator to effect switching of input/output ports formed in a sleeve.
The electromagnetic actuator is provided with a first volume varying chamber on a stator (a member for attracting a plunger magnetically) of a plunger and is also provided with a second volume varying chamber on an opposite side of the first volume varying chamber of the plunger.
On the other hand, the spool valve is provided with a third volume varying chamber on the electromagnetic actuator side of the spool and is also provided with a fourth volume varying chamber on an opposite side of the third volume varying chamber of the spool.
The plunger and the spool are adapted to displace axially integrally. Such axial displacement of the plunger and the spool causes a change in volume of the first to fourth volume varying chambers. One or multiple breathing holes communicating with an external oil path are formed in the sleeve. The breathing hole(s) and the first to fourth volume varying chambers are in communication with each other through a breathing passage. With the breathing hole and the breathing passage, oil can be supplied to the first to fourth volume varying chambers, whereby the plunger and the spool can move axially.
As described above, upon movement of the plunger and the spool, oil is supplied or discharged to the first to fourth volume varying chambers through the breathing hole and the breathing passage.
As a result, foreign matters (wear dust, etc.) contained in the oil are carried into the first to fourth volume varying chambers together with the oil.
The first and second volume varying chambers are formed in the interior of the electromagnetic actuator, and when magnetic foreign matters (e.g., iron powder and iron pieces) get into the both chambers, they may constitute a part of a magnetic circuit. Once this occurs, the magnetism acting on the plunger loses balance and a force acts on the plunger in a direction perpendicular to the axis of the plunger. As a result, the plunger slides strongly against a member (e.g., a cup guide for oil seal) located around the plunger and its movement in its axial direction is obstructed, with a consequent likelihood that characteristics required of OCV may become unable to obtain.
Even a foreign matter which is not a magnetic foreign matter may be deposited in the first and second volume varying chambers and obstruct the movement of the plunger, with a consequent likelihood of OCV becoming inoperative.